This question isn't so much about FTP or even Yummy FTP, but more a question of how your web site is set up and/or your web hosting provider has things set up, and as such you should really contact your web hosting provider for assistance, but I will try to help... So, it's hard for me to say exactly what needs to be done, but in general, web sites have a home page which is accessed by the file "index.html". If you have an index.html file for your web site and you have uploaded it, make sure that it replaced the existing index.html file that is already there. Since the web site still says "under construction" I can only assume that the index.html file did not get replaced, so perhaps you should check to see where it is in the server listing - maybe it is in a sub folder named www for example. If that is the case, then you have uploaded all the files to the wrong place and you should move them.
Have a look again and see if you can figure it out from what I've said above. If you're still stuck, email me (support at yummysoftware dot com) and let me know your server connection details (server name/ip, username and password) and I will have a look for you and tell you what to do

-Jason